CN110760771B

CN110760771B - Hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics and manufacturing method thereof

Info

Publication number: CN110760771B
Application number: CN201810842261.6A
Authority: CN
Inventors: 谭宁; 金鑫焱; 钟勇; 魏军胜
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2018-07-27
Filing date: 2018-07-27
Publication date: 2022-07-22
Anticipated expiration: 2038-07-27
Also published as: CN110760771A

Abstract

The hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics comprises a substrate, an Fe-Al alloy layer and a zinc coating layer in sequence, wherein the substrate comprises the following chemical components in percentage by weight: c: 0.15 to 0.25 wt%, Si: 1.00-2.00 wt%, Mn: 1.50-3.00 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.012 wt%, Al: 0.03-0.06 wt%, the balance being Fe and unavoidable impurities; the area of the missing region of the Fe-Al alloy layer is less than 5 percent, the Fe-Al alloy layer is uniform and complete and has consistent appearance characteristics, and the hot-galvanized steel plate obtained after hot galvanizing has good appearance quality and does not have the defects of plating leakage, pocking mark, color difference and the like, and is suitable for automobile structural parts and outer plates with higher requirements on surface quality and formability.

Description

Hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics and manufacturing method thereof

Technical Field

The invention belongs to the technical field of hot-dip galvanized steel plates, and particularly relates to hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics and a manufacturing method thereof.

Background

When hot dip coating pure zinc (without aluminum) is performed on a steel sheet, the alloy layer formed by the Fe — Zn reaction is thick and brittle, so that the workability is poor, and the zinc layer is likely to be peeled off during bending deformation. In order to inhibit the growth of the Fe-Zn alloy layer in a modern continuous hot dip galvanizing line, a small amount of aluminum (about 0.2%) is added to a zinc bath, and since the chemical affinity of aluminum to iron is higher than that of zinc to iron, a selective reaction occurs on the surface of a steel sheet, and a thin Fe-Al alloy layer is formed first, thereby inhibiting the diffusion of zinc.

At present, the demand for lightweight automobiles is becoming stronger, and the development of high strength and high toughness of automobile steel is forced. In order to improve the strength and toughness of the substrate, alloy elements such as Si, Mn, Cr, and Al are often added to the substrate, and although these alloy elements can make the substrate obtain good mechanical properties, these alloy elements often concentrate on the surface of the steel sheet in the form of oxides before the annealing stage of hot galvanizing, which causes non-uniformity of the components and states of the substrate surface, thereby affecting the formation and characteristics of the Fe-Al alloy layer during hot galvanizing.

Chinese patent CN103805840A discloses a high-formability hot-dip galvanized ultrahigh-strength steel plate, which can improve the platability by optimizing the heating section and heat preservation section processes and the dew point atmosphere to obtain a hot-dip galvanized product, but the surface quality of the actual hot-dip galvanized product fluctuates, is greatly influenced by microscopic changes of the surface state of incoming materials, has high difficulty in on-site production, and often causes the problems of plating leakage, pocking marks, color difference and the like, and is mainly due to the fact that Fe-Al alloy layers between a plating layer and a substrate are missing or discontinuous.

Chinese patent 201480008243.8 discloses a coated steel substrate for hot dip galvanizing, which contains 0.01-1% of C, 0.15-15% of Mn, 0.005-3.5% of Si, 0.01-2% of Al and 0.01-2% of Cr, two layers of pre-plating treatment are carried out before hot dip galvanizing, the first pre-plating layer takes Cu as a main component, the second pre-plating layer takes Fe as a main component, the first pre-plating layer Cu is considered to mainly improve the oxide enrichment on the surface of a steel plate, but Cu can pollute a zinc liquid, and Cu can not form a good Fe-Al alloy layer with the zinc liquid, so that the adhesion of the subsequent plating layer is influenced, so that the Fe of the second pre-plating layer is increased, the pollution of Cu is reduced on one hand, and the other hand, the purpose of forming the Fe-Al alloy layer is achieved, and the good adhesion of the plating layer is ensured. It also discloses that if direct pre-plating of Fe requires a thicker pre-plating layer (greater than 800nm) to suppress the enrichment of oxides on the steel sheet surface, and that the Fe plating layer is not suitable for reducing the enrichment of Mn oxides. The patent uses a two-layer pre-plating process, which not only increases the cost, but also cannot be well matched with a hot galvanizing process, and the two-layer pre-plating and hot galvanizing are difficult to be simultaneously realized in the same unit, so the actual production difficulty is higher.

Disclosure of Invention

The invention aims to provide hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics and a manufacturing method thereof, wherein a continuous Fe-Al alloy layer is arranged between a coating and a substrate of the hot-dip galvanized steel sheet, the area of a missing region of the Fe-Al alloy layer is less than 5%, the Fe-Al alloy layer is uniform and complete, the appearance characteristics are consistent, the hot-dip galvanized steel sheet obtained after hot dip galvanizing has good appearance quality and no defects of plating leakage, pockmarks, color difference and the like, and the hot-dip galvanized high-strength steel is suitable for automobile structural parts and outer plates with higher requirements on surface quality and formability.

In order to achieve the purpose, the technical scheme of the invention is as follows:

according to the invention, before annealing and hot galvanizing are carried out on high-strength steel, a layer of metal Fe is pre-plated, then an annealing process is reasonably set, and the Fe content on the surface of the substrate is ensured to be more than 95 wt%, and the sum of the contents of Si and Mn is less than 2 wt% before the substrate enters a zinc liquid, so that an excellent Fe-Al alloy layer is obtained on the surface of a steel plate.

Specifically, the hot dip galvanized high-strength steel with excellent characteristics of the Fe-Al alloy layer sequentially comprises a substrate, the Fe-Al alloy layer and a zinc coating; the substrate comprises the following chemical components in percentage by weight: c: 0.15 to 0.25 wt%, Si: 1.00-2.00 wt%, Mn: 1.50-3.00 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.012 wt%, Al: 0.03-0.06 wt%, the balance being Fe and unavoidable impurities; the Fe-Al alloy layer is uniform and complete and has consistent appearance characteristics, and the area of the missing region of the Fe-Al alloy layer is less than 5%.

Furthermore, the hot-dip galvanized high-strength steel has yield strength of 600-900 MPa, tensile strength of 980-1200 MPa and elongation of 15-22%.

The invention also provides a manufacturing method of the hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics, which comprises the following steps:

1) pre-plating Fe treatment

Performing pre-plating Fe treatment on the substrate, and forming a metal Fe layer on the surface of the substrate after the pre-plating Fe treatment; the substrate comprises the following chemical components in percentage by weight: c: 0.15 to 0.25 wt%, Si: 1.00-2.00 wt%, Mn: 1.50-3.00 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.012 wt%, Al: 0.03-0.06 wt%, the balance being Fe and unavoidable impurities;

2) annealing treatment

Preheating a substrate to 600-650 ℃; preserving the heat for 40-80 s at 780-820 ℃, and H in an annealing furnace₂The content is 3-7.5%; cooling to 700-800 ℃ at the speed of 3-10 ℃/s, then cooling to 230-340 ℃ at the speed of more than or equal to 50 ℃/s, and then heating to 455-465 ℃;

3) and (4) hot-dip galvanizing.

Further, in the step 1), the Fe treatment method is an electrochemical Fe plating method or a vacuum Fe plating method.

In the step 1), the thickness of the metal Fe layer is 100-400 nm.

In the step 3), the zinc liquid of the hot dip galvanizing is Zn, Zn-Al-Mg or Zn-Al-Mg + X, and the X comprises at least one of other metals such as Si, Ca, Sr, Ba, rare earth elements and the like.

The surface components of the hot-dip galvanized high-strength steel substrate after being subjected to pre-plating Fe treatment and annealing treatment are mainly Fe, the Fe content is higher than 95 wt%, and the total content of Si and Mn is lower than 2 wt%.

After the hot dip galvanized high-strength steel substrate manufactured by the invention is subjected to pre-plating Fe treatment, a metal Fe layer is formed on the surface of the substrate, and the annealing process ensures that the surface of the substrate mainly contains Fe with the Fe content higher than 95 wt% and the total content of Si and Mn lower than 2 wt% before the substrate is added into zinc liquid, so that an excellent Fe-Al alloy layer is obtained on the surface of the steel plate.

The area of the deletion area of the Fe-Al alloy layer is less than 5%, the Fe-Al alloy layer is uniform and complete and has consistent appearance characteristics, and the Fe-Al alloy layer has excellent characteristics. Therefore, the hot dip galvanized steel sheet obtained after hot dip galvanizing has good appearance quality, no defects of plating leakage, pockmarks, color difference and the like, is integrally continuous, has uniform thickness and consistent appearance characteristics.

The invention has the beneficial effects that:

the existence of the metal Fe layer on the surface of the substrate can inhibit the enrichment of alloy elements Si, Mn oxides and the like on the surface of the substrate in the annealing process, thereby reducing the content of Si and Mn oxides on the surface of the substrate, improving the content of Fe on the surface of the substrate, improving the effective contact of the substrate and zinc liquid in the hot galvanizing process and being beneficial to the formation of an Fe-Al alloy layer.

The pre-plating Fe treatment does not completely inhibit the enrichment of Si and Mn oxide on the surface, and allows a small amount of oxide to exist, namely a small amount of iron oxide, silicon oxide, manganese oxide or silicon-manganese oxide exists on the surface of the annealed substrate, and the residual oxide is discontinuously distributed and exists in an isolated island shape, so that the formation of an Fe-Al alloy layer is not influenced. Therefore, the pre-plated Fe layer can meet the platability of the steel plate under the condition of lower thickness (the thickness of the Fe layer is less than or equal to 600 nm).

The invention can improve the contact between the substrate and the zinc liquid by adding the pre-plated Fe layer and controlling the annealing process, and simultaneously optimize the thickness of the metal Fe layer and the annealing process, thereby maximizing the effects of the metal Fe layer and the annealing process, which is difficult to achieve by independently controlling the pre-plated Fe layer or the annealing process.

The mechanism that the preplating Fe treatment can improve the platability of the steel plate is that a preplated metal Fe layer with a certain thickness occupies the surface of the steel plate, the Fe layer can occupy the positions of Si and Mn elements in a base plate in the annealing process of the steel plate, meanwhile, the annealing process control of the invention further reduces the diffusion of the Si and Mn elements to the surface of the base plate, thereby increasing the enrichment difficulty of the Si and Mn elements on the surface, and even if a small amount of Si and Mn elements exist in local positions, the preplated Fe layer can still occupy most of the surface, so that Fe can react with plating solution through Fe-Al in the subsequent hot-dip galvanizing process, thereby forming a continuous Fe-Al alloy layer.

The Fe-Al alloy layer in the hot-dip galvanized steel sheet is uniform and continuous, has consistent appearance characteristics, greatly contributes to the surface quality of the hot-dip galvanized steel sheet, can greatly reduce quality defects of surface pocking marks, plating leakage, color difference and the like, simultaneously improves the adhesive force of a plating layer, and can meet various complex forming requirements of the hot-dip galvanized steel sheet.

The hot dip galvanized steel sheet has the characteristics of high strength and high toughness, the yield strength is 600-900 MPa, the tensile strength is 980-1200 MPa, the elongation is 15-22%, and the hot dip galvanized steel sheet has a good application prospect on automobile structural members and outer plate members with high requirements on surface quality and formability.

Drawings

FIG. 1 is a scanning electron microscope image of the surface of the Fe-Al alloy layer at the plating missing defect of the hot-dip galvanized steel sheet prepared in comparative example 1.

FIG. 2 is an appearance view of a hot-dip galvanized steel sheet produced in example 2 of the present invention.

FIG. 3 is a scanning electron microscope image of the surface of the Fe-Al alloy layer of the hot dip galvanized steel sheet prepared in example 2 of the present invention.

FIG. 4 is a depth profile of the elements of the hot dip galvanized steel sheet prepared in example 2 of the present invention.

Detailed Description

The invention is further illustrated by the following examples and figures.

Table 1 shows the composition of the hot-dip galvanized steel sheet according to the present invention. Table 2 shows the annealing process and the hot-dip galvanized steel sheet performance of the hot-dip galvanized steel sheet according to the invention.

FIG. 1 is a scanning electron microscope image of the surface of an Fe-Al alloy layer at a plating-missing defect of direct annealing hot galvanizing without pre-plating Fe treatment in comparative example 1. It can be seen from FIG. 1 that the Fe-Al alloy layer is discontinuous and lacks in a large area.

FIG. 2 is the appearance of the galvanized sheet after the pre-plating Fe treatment in example 2, and compared with the non-pre-plating Fe treated part, it can be seen that the surface quality of the galvanized sheet after the Fe layer plating is better, and the surface of the steel sheet without the pre-plating Fe layer has obvious plating missing points.

FIG. 3 is a scanning electron microscope image of the surface of the Fe-Al alloy layer of the hot dip galvanized steel sheet prepared in example 2. As can be seen from FIG. 3, the Fe-Al alloy layer is completely continuous.

FIG. 4 is a depth profile of elements of a hot dip galvanized steel sheet prepared in example 2. As can be seen from FIG. 4, a distinct Al-enriched layer, i.e., a Fe-Al alloy layer, is present at the interface, and no distinct Si and Mn element enrichment is found at the interface.

Claims

1. The hot-dip galvanized high-strength steel with the excellent Fe-Al alloy layer characteristic sequentially comprises a substrate, an Fe-Al alloy layer and a zinc coating, and is characterized in that the substrate comprises the following chemical components in percentage by weight: c: 0.15 to 0.25 wt%, Si: 1.00-2.00 wt%, Mn: 1.50-3.00 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.012 wt%, Al: 0.03-0.06 wt%, the balance being Fe and unavoidable impurities; the area of the deletion region of the Fe-Al alloy layer is less than 5 percent; the base plate is processed by pre-plating Fe, the Fe content in the surface components of the base plate is more than 95 wt%, and the sum of the contents of Si and Mn is less than 2 wt%.

2. The hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics according to claim 1, wherein the yield strength, tensile strength and elongation of the hot-dip galvanized high-strength steel are 600-900 MPa, 980-1200 MPa and 15-22%.

3. The method for manufacturing hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics according to claim 1 or 2, comprising the steps of:

1) pre-plating with Fe

Performing pre-plating Fe treatment on a substrate, and forming a metal Fe layer on the surface of the substrate after the pre-plating Fe treatment, wherein the thickness of the metal Fe layer is 50-600 nm;

the substrate comprises the following chemical components in percentage by weight: c: 0.15 to 0.25 wt%, Si: 1.00-2.00 wt%, Mn: 1.50-3.00 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.012 wt%, Al: 0.03-0.06 wt%, the balance being Fe and unavoidable impurities;

2) annealing treatment

Preheating the substrate to 600-650 ℃; preserving the heat for 40-80 s at 780-820 ℃, and H in an annealing furnace₂The content is 3-7.5%; cooling to 700-800 ℃ at the speed of 3-10 ℃/s, then cooling to 230-340 ℃ at the speed of more than or equal to 50 ℃/s, and then heating to 455-465 ℃;

3) and (4) hot-dip galvanizing.

4. The method of claim 3, wherein the Fe treatment method in step 1) is an electrochemical Fe plating method or a vacuum Fe plating method.

5. The method for manufacturing hot dip galvanized high strength steel with excellent Fe-Al alloy layer characteristics according to claim 3 or 4, wherein in the step 1), the thickness of the metallic Fe layer is 50 to 600 nm.

6. The method for manufacturing hot dip galvanized high tensile steel having excellent Fe-Al alloy layer characteristics according to claim 3, wherein in the step 3), the molten zinc for hot dip galvanizing is Zn, Zn-Al-Mg or Zn-Al-Mg + X, and X includes at least one of Si, Ca, Sr, Ba and rare earth elements.

7. The method for manufacturing the hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics according to claim 3, wherein the Fe content in the surface component of the hot-dip galvanized high-strength steel substrate after being pre-plated with Fe and annealed is more than 95 wt%, and the sum of the contents of Si and Mn is less than 2 wt%.

8. The method for manufacturing the hot-dip galvanized high-strength steel with excellent Fe-Al alloy layer characteristics according to any one of claims 3 to 7, wherein the yield strength, the tensile strength and the elongation of the hot-dip galvanized high-strength steel are 600-900 MPa, 980-1200 MPa and 15-22%, respectively.